Power distribution circuits typically used by electric utilities can experience various faults that disrupt service to consumers of electricity. Causes of such faults include electrical insulation breakdown or mechanical failures. Most commonly, faults are manifested as short circuits from line to ground, but line to line short circuits and open circuit faults can also occur. When these events occur, they are readily detectable and safety devices, such as circuit breakers, can be automatically actuated to shut down the distribution circuit. It is important for the utility and its customers to have the problem located and repaired as quickly as possible so that electrical service can be restored with minimal down time. In practice, since power transmission or distribution circuits extend over large distances, repair crews must patrol the entire line section. Locating faults is thus presently time consuming and expensive due to the lost revenue and the cost of lengthy troubleshooting.
Systems known in the art for localizing power line faults include stand-alone (independently-functioning) fault detectors deployed on distribution feeders that emit light or audible alarm signal when they detect an abnormally high current magnitude. This approach does not eliminate the need for repair crews to examine long stretches of power line as part of troubleshooting a line fault.
There are other devices known in the art that can be equipped with contact outputs for use with a SCADA system, but it appears that no integrated system approach exists to date for localizing faults potentially occurring over a long stretch of power line.
Another problem experienced by utilities involves a reverse EMF generated by certain loads in a power outage. Motorized equipment and appliances (air conditioners, for example) that are loads on a broken distribution circuit can, following a fault, generate an EMF in the broken circuit section that appears as a flow of power from the load in a direction opposite the ordinary flow of power during normal system operation. For example, in the case of a line fault affecting one of three phases of a power distribution circuit, a three-phase motor powered by the remaining two phases will continue running, and may well operate as a power generator producing an EMF back onto the wire of the faulty phase. Measuring line current magnitude, alone, near the fault point, is therefore sometimes insufficient to distinguish between an actual fault and a momentary imbalance of the distribution circuit.
Yet another drawback associated with conventional current measuring devices are the hazards associated with installing the devices on the high voltage power lines.